The invention relates to a bottle top dispenser with a valve housing and with a piston-cylinder unit, which can be releasably affixed to the housing, the piston and cylinder of which can be activated in an axial stroke movement relative to one another, in order to draw liquid from a bottle on which the dispenser is set, and eject it, where the intake process takes place in a spring-activated extension movement and the ejection process takes place in a manually activated compression movement of the piston-cylinder unit.
Such bottle top dispensers are known from practice. They are particularly used to repeatedly dispense an adjustable liquid volume from a bottle.
It is known that the piston-cylinder unit of a bottle top dispenser can be designed as an interchangeable part. Therefore it is provided that the piston-cylinder unit be affixed on the valve housing of the dispenser in releasable manner.
Piston-cylinder units designed as interchangeable parts can be cost-effectively produced by injection-molding of plastic. The requirements with regard to their durability are not as high as for dispensers with permanently installed piston-cylinder units.
Piston-cylinder units designed as interchangeable parts open up the possibility of equipping the valve housing of the dispenser with piston-cylinder units of different sizes, depending on the volume of liquid to be dispensed. Also, different types of liquid to be dispensed can have their own piston-cylinder units assigned to them, and they can be exchanged when the liquid is changed. This simplifies the work process, and high requirements with regard to purity are fulfilled with less effort.
The interchangeability of the piston-cylinder units is particularly important when working under sterile conditions and when handling radioactive substances. For hygiene reasons and for the sake of work place safety, it can be necessary to dispose of contaminated piston-cylinder units in the proper manner, rather than cleaning them.
The known bottle top dispensers are designed for one-hand operation. In the case of dispensers with a high intake force, a spring element, generally referred to as an intake spring, between the piston and the cylinder of the piston-cylinder unit serves for this purpose, to move the latter out in order to draw in liquid. To eject the liquid, the piston-cylinder unit is moved in by hand again, and during this process, the intake spring is tensed for the next intake stroke.
In piston-cylinder units designed as interchangeable parts, there is a problem with the intake spring.
On the one hand, dispensers are known in which the user must remove a helical pressure spring, which serves as the intake spring, from the old piston-cylinder unit, and clamp it in between the piston and the cylinder of the piston-cylinder unit, when the piston-cylinder unit is being replaced. This requires skill, time and effort. It is all too easy for the spring to jump away and become lost. There is also the risk of getting the piston-cylinder unit dirty.
On the other hand, dispensers in which each of the piston-cylinder units designed as interchangeable parts has its own intake spring are possible. But that would involve a lot of material and high costs, and there would be additional effort connected with disposal.
The problem with the intake spring is a serious one, and a major reason is that the spring must be quite strong. The spring is accordingly difficult to handle when replacing the piston-cylinder unit, and it is too good to be thrown away when replacement occurs.